CDC Revises HIV Testing Guidelines to Better ID Early Cases

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The Centers for Disease Control and Prevention (CDC) has recommended a new HIV testing protocol for laboratories that will take advantage of advances in testing technology and will better identify acute cases of the virus. The announcement was made to coincide with National HIV Testing Day on June 27.

New “fourth generation” HIV tests not only screen for antibodies to the virus in blood samples but also for what’s known as the HIV-1 p-24 antigen, which shows up in the body much sooner than antibodies. By recommending the fourth generation tests as the first step in the new testing protocol, the CDC will effectively reduce the “window period” during which false negatives are likely. The new tests will detect an infection by about three weeks following exposure to the virus; with the older HIV tests, the window period could be as long as three months. Correctly identifying acute cases of HIV is crucial for HIV prevention because viral loads are typically very high during that period of infection, making someone much more likely to pass on the virus.

If the initial HIV test is positive, the next step is to perform an HIV-1/HIV-2 antibody differentiation immunoassay in order to determine if the individual is carrying HIV-1 or HIV-2. This test will produce results faster than the previously recommended Western Blot screen.

If there is a negative or indeterminate result of the second testing step, then the CDC recommends a nucleic acid test. A negative result of that test indicates a false positive result on the earlier test, meaning that the individual does not have HIV. A positive result indicates an acute infection.

“HIV testing is the linchpin for prevention and treatment,” Jonathan Mermin, MD, MPH, director of the National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention at the CDC, said in a release. “For people who test HIV positive, diagnosis opens the door to lifesaving treatment, which also reduces the risk of transmitting HIV to others. For those who test negative, knowing their status empowers them to remain HIV-free.

“However, more than half of American adults still have never been tested for HIV. Nearly one in six people living with HIV in the United States do not know they have HIV, meaning that they are missing out on essential care and may unknowingly transmit the virus. Roughly half of the estimated 50,000 new HIV infections each year are transmitted by people who don’t know that they are HIV positive.”